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Class 20

Class 20. Series feedback H calculation in case of S-V and S-C f.b. Transfer parameters (gains) Input resistance Parallel feedback H calculation in case of P-V and P-C f.b. Transfer parameters (gains) Input resistance. Class 20. Output resistance

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Class 20

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  1. Class 20 • Series feedback • H calculation in case of S-V and S-C f.b. • Transfer parameters (gains) • Input resistance • Parallel feedback • H calculation in case of P-V and P-C f.b. • Transfer parameters (gains) • Input resistance

  2. Class 20 • Output resistance • In the case of series voltage feedback • If Rg = 0 • If Rg  0 • In the case of parallel current feedback • If Rg =  • If Rg  • Without derivation, the formulas for the remaining two cases

  3. Class 20 • Numeric problems • Problem 1 • For an asymmetrical amplifier: Rin=12k , RL= 5 Ro. Applying P-V feedback, we measure the Ro* : • at Rg1=12 k, Ro1*=250 and • at Rg2=24 k, Ro2*=200. • Find Ro and Rin*.

  4. Class 20 • Applying the Ro* formula, solving a system of equations, we get: HSp = 6 and Ro = 1kΩ. • From HSp the H can be calculated and with this the input resistance: H = 5 and Rin*=72kΩ.

  5. Class 20 • Problem 2 • The parameters of an asymmetrical amplifier: Avoc=160, Rin=10kΩ, Rout=1kΩ; input and output closing resistances: Rg=1kΩ, RL = 15 kΩ. • Prescribed parameters: Av* = 10, Rin*  100 kΩ, Rout*  0,15 kΩ. • Tasks: • a.) the type of the necessary feedback; • b.) the transfer factor of an ideal feedback; • c.) checking the prescribed parameters.

  6. Class 20 • Solution: • a.) Rin*  Rin series feedback • Rout*  Rout voltage feedback • So the applied arrangement: S-V feed-back • b.) Calculating • Av (from Av oc): Av=150 • H (from Av* and Av): H=14 • And ß (from H and Av): ß=14/150 • Rin* =…=150kΩ; Rout*=…=0.073kΩ (ain=10/11) • c.) Both ar OK

  7. Class 20 • INFORMATION • Next week on Thursday (April 17) the 2nd Mid-Term-Test is coming. Some problems from the previous years will be shown before that (onApril 14).

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